Convertible snow plow with auxiliary ground support

ABSTRACT

A snow plow attachable to the front of a truck or other vehicle. A moldboard assembly is supported by hydraulic jacks on groundengaging members such as caster wheels or shoes and is connected by a thrust frame to a hitch on the vehicle. A moldboard has two separate blades each having a ground-engageable scraping edge. One blade is steel, fixed along the lower portion of the moldboard. The other blade is rubber-like and is movable to an extended, working position below the steel blade, enabling it to act as a squeegee to clear soft snow and slush. The rubber-like blade is also movable to a stowed position above the scraping edge of the steel blade, enabling the steel blade to engage the ground when a harder, general purpose cutting edge is required. Pressure applied to the hydraulic jacks exerts a lifting force on the moldboard assembly through the ground-engaging members. Pressure is regulated by a relief valve which is adjustable to transfer a definite, predetermined portion of the moldboard assembly weight to the ground-engaging members. By adjusting the relief valve, heavy cutting pressure, or light squeegee pressure, may be applied through the moldboard assembly as required by the steel or rubber-like blade.

United StatesPatent [191 Snyder CONVERTIBLE SNOW PLOW WITH .AUXILIARY GROUND SUPPORT [75] Inventor:

[52] US. Cl 37/42 R, 172/277, 172/413,

172/805 [51] Int. Cl E0lh 5/04 [58] Field of Search..... 37/41, 42 R, 42 VL, 50, 44, 37/46; 172/276, 801-809, 277, 464, 4, 4.5, 395, 397, 398, 407, 413, 779

[56] References Cited UNITED STATES PATENTS 3,560,023 2/1971 Norton et a1. 172/464 X 2,913,878 11/1959 Rue 172/4 X 1,424,128 7/1922 Ziegler 172/413 1,964,617 6/1934 Bird 37/42 R 3,466,766 9/1969 Kahlbacher.. .....'37/50 X 2,882,623 4/1959 Gardner 172/784 3,705,631 12/1972 Seaberg 172/809 3,307,275 3/1967 Simi 37/42 R 2,778,126 l/l957 Shannon 37/42 R 2,721,405 10/1955 Gardner 172/784 2,055,291 9/1936 Henry 37/42 R 2,061,585 11/1936 Meyer 37/42 3,413,738 12/1968 Goldberg 37/42 3,126,652 3/1964 Reissinger 37/42 VL FOREIGN PATENTS OR APPLICATIONS 264,572 9/1968 Austria 37/42 VL {451 Feb. 26, 1974 Primary Examiner--Robert E. Pulfrey v Assistant Examiner-Eugene I-l. Eickholt Attorney, Agent, or Firm- Davis, McCalleb & Lucas 5 7] ABSTRACT A snow plow attachable to the front of a truck or other vehicle. A moldboard assembly is supported by hydraulic jacks on ground-engaging members such as caster wheels or shoes and is connected by a thrust frame to a hitch on the vehicle. A moldboard has two separate blades each having a ground-engageable scraping edge. One blade is steel, fixed along the lower portion of the moldboard. The other blade is .rubber-like and is movable to an extended, working position below the steel blade, enabling it to act as a squeegee to clear soft snow and slush. The rubber-like blade is also movable to a-stowed position above the scraping edge of the steel blade, enabling the steel blade to engage the ground when a harder, general purpose cutting edge is required. Pressure applied to the hydraulic jacks exerts a lifting force on the moldboard assembly through the ground-engaging members. Pressure is regulated by a relief valve-which is adjustable to transfer a definite, predetermined portion of the moldboard assembly weight to the groundengaging members. By adjusting the relief valve, heavy cutting pressure, or light squeegee pressure, may be applied through the moldboard assembly as required by the steel or rubber-like blade.

7 Claims, 8 Drawing Figures BACKGROUND OF THE INVENTION The field of the invention is a vehicle-carried snow plow, particularly a snow plow attachment for the front of a vehicle such as a truck. For general purposes, a moldboard assembly having a steel scraping blade engageable with the ground is commonly used. Where the most complete removal ofsoft snow and slush is required, as for example on airport runways or shopping center parking lots, rubber-like scraping blades are used. An example of special purpose moldboard assemblies using a rubber-like blade is Reissinger US. Pat. No. 3,126,652 issued Mar. 31, 1964 on ROAD CLEARING APPLIANCE.

Past attempts to use rubber-like scraping edges on snow plows have not been entirely satisfactory. If a rubber-like blade is merely substituted in a moldboard assembly designedfor a steel blade, the weight of the moldboard assembly pressing the rubber-like blade against the ground causes it to wear excessively. Attempts to regulate the pressure of the rubber-like blade against the ground by adjusting the elevation of the moldboard on the main frame have not solved the problem of wear on the blade because even the best paved surfaces have up and down undulation causing the high portions to scuff and tear the blade.

As a practical matter, snow plows using rubber-like blades have had to be. specially designed and constructed to maintain the moldboard at some fixed height above the ground, and attach the rubber-like blade across the bottom edge in such a way that the ground contacting portion is free to flex or fioat up and down with the undulations in the surface being cleared. This requires'a special design and the entire moldboard assembly has to be replacedif conditions call for a heavy steel cutting edge where ice and hard-packed snow must be cleared.

Prior to the present invention, no one has developed an easily usablesnow plow which is readily convertible for hard-packed snow requiring a steel cutting edge, and for soft snow or slush requiring a rubber-like scraping edge.

SUMMARY OF THE INVENTION A general object of the present invention is to provide a single snow plow apparatus which is readily convertible for clearing hard snow or ice, and for soft snow or slush.

Another object is to provide a convertible snow plow in which a steel blade or a rubber-like blade isusabIe at the operators option.

-A further'object is to provide a snow 'plow with a moldboard assembly having two blades with optionally I usable scraping edges selectively engageable with the caster wheels or shoes, and pressure to the hydraulic jacks can be regulated by adjusting a relief valve to transfer a definite predetermined portion of the moldboard assembly weight to the caster wheels or shoes, depending on the ground pressure requirements for the steel blade or the rubber-like blade.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages will be apparent from the following description taken in connection with the drawings in which:

FIG. 1 is a fragmentary side view of a truck supporting a convertible snow plow illustrating a preferred form of the present invention;

FIG. 2 is an enlarged top view of the convertible snow plow shown in FIG. 1, illustrating the apparatus in a diagonal operating position; 1

FIG. 3 is an enlarged view of the convertible snow plow and hitch shown in FIG. 1, illustrating the rubberlike blade in its extended, operating position;

FIG. 4 is a fragmentary view similar to FIG. 3 showing the rubber-like. blade in its stored, non-operating position, enabling the steel scraping blade to engage the ground;

FIG. 5 is an enlarged, fragmentary, vertical sectional view of FIG. 2 taken along the line 5-5;

FIG. 6 is a fragmentary, partly sectional, rear view of the convertible snow plow taken along line 6-6 of FIG. 3;

FIG. 7 is a side view similar to FIG. 3 but on a much smaller scale, indicating displacement of plow components upon striking an obstruction in the roadway; and

FIG. 8 is a hydraulic diagram.

Like parts are referred to by like reference characters throughout the figures of the drawings.

Referring now more particularly to the embodiment shown in the drawings, a truck 20 has a hitch22' mounted at the front. This supports a convertible snow plow 24 illustrating a preferred form of the present invention.

The hitch 22 is conventional, having an upright frame including a pair of supporting columns 26, cross-braced by transverse tie members 28 and 30, among others not shown, and fastened to the front bumper and frame of the truck, A lift arm 32 is movable up and down about the pivot pin 34 by a lift cylinder 36, the opposite ends of which are pivoted on pins 38 and 40 carried respectively on the lift arm 32 anda pivot block 42 mounted on the center of the tie member 28. A clevis link 44 is pivoted on a pin 47 at the end of arm 32 and supports a sheave 46 on a journal pin 48.

Major components and subassemblies of the convertible snow plow 24 include: a thrust frame 50 pivoted on the hitch 22 for "up-and-down movement about the transverse horizontal axis 52; a leveling frame 54 is pivoted on the thrust frame for turning movement about the longitudinal axis 56 (FIG. 5); a reversing frame 58 pivoted on the leveling framefor horizontal swinging movement about the uprightaxis '60; and a moldboard assembly 62 pivoted on the reversing frame for up-anddown movement about a'transverse horizontal axis 64.

As best shown in FIGS. 3 and 5, the thrust frame 50 comprises a horizontal, transversely extending box member 66 having a flat, forward bearing surface 68.

' A vertical gib 70, at each horizontal end of the bearing surface 68, is spaced slightly forward to provide a retaining pocket 72 for a corresponding one of the retaining ears 74 on the leveling frame 54. A pair of pushplates 76 are fastened by bolts 78 to the ends of the box member 66. Each pushplate has a bearing opening 80 pivotally journaled about a hinge pin 82 carried by one of the columns 26. Pins 82 are aligned along axis 52.

The leveling frame 54 is triangular in 'plan view (FIG. 2), having a flat bearing surface 83 along the base, and a pair of sides 84, 84 tapering toward a narrow forward end 86.

An arched anchor member 88 is mounted on the top plate 90 of the leveling frame 54. It has two functions: it provides a central, fixed pivor axis 60 for reversing cylinders, to be described; and it provides a hold-down and lock for the rear swinging end of the reversing frame 58, to be described. The anchor member 88 may be a weldment or casting and has, at its forward end, a pad 92 fastened to the leveling frame surface 90 by four bolts 94. At its rear end, there is another pad 96 held by two bolts 98 ahd having vertical reinforcements 99. At the extreme rear end portion of the pad 96, there is an underside recess 100 for retaining the swinging end of the reversing frame as will be described. The arched midsection of the anchor member 88 has a vertical bearing sleeve 102 for pivotally anchoring the reversing cylinders as will be described.

The thrust frame 50 and leveling frame 54 are assembled with their bearing surfaces 68 and 83 in flatwise abutment, and the, ears 74 retained within pockets 72. The two frames are held so assembled, and relatively pivotable about longitudinal axis 56, by a pivot bolt 104 extending through longitudinal center bores 106 and 108 respectively. A nut 1 on the endof the bolt holds the two frames securely, but relatively pivotable.

Near its narrow forward end 86, the leveling frame 54 has a vertical sleeve bearing 112 aligned with the upright axis 60. This provided a swingable support for the reversing frame 58 as will be described.

The reversing frame 58 comprises a transverse channel member 114, with a generally U-shaped cross section. It has a forward, vertically disposed base 1 l6 and spaced upper and lower webs 118 and 120. The back may be closed for additional strength, or may be left open as shown, except where the forward apex end 86 is fitted into it. (See FIG. 5.)

A subframe 122, generally in the shape of a flatbottomed V, is fastened as by welding to the upper web 118 of the reversing frame. This subframe consists of two backwardly converging angle sections 124 joined by a central, transverse angle section 128. Brackets 130 are positioned at the forward ends of angle sections 124 and are fastened in place by welding to both the angle sections and the channel member 114. These brackets 130 provide pivotal connections for the reversing cylinders as will be described.

At each end of the transverse channel member 114, there is a short, transverse, vertical flange 134 along the back edge of the upper web 118. This is held in place and the entire end structure of the reversing frame rigidified by welding to the web 1 18, to the vertical webs of angle sections 124, and to a reinforcing end plate 136 which is welded across each end of the channel member 114.

At each transverse end of the channel member 114, that is, at each side of the reversing frame 58, the upwardly open end portion of web 118 comprises a seat or bearing 138 for a spring retainer to be described. It is defined on two sides by vertical plates 134 and 136 and has a pair of openings 140 for a purpose to be described.

Along the forward edge of the reversing frame, that is, along the base 116 of channel member 114, there are three aligned hinge members to provide pivotal support for the moldboard. Two of these, at the sides, are designated 142 and have hinge pin receiving openings 144. The third hinge member comprises a pair of hinge elements 142a with hinge pin receiving openings 144a.

Bolted to the back side of each short vertical flange 134, by bolts 146 is a vertical mounting plate 148, on which is mounted a vertically disposed hydraulic jack 150. The jack comprises a cylinder 152. This is fastened to the vertical mounting plate 148 by a pair of vertical strips or angles 154 which are fastened as by welding to both the cylinder 152 and the plate 148. Where desired, the cylinder 152 may beadjusted as to height by moving it up or down on the flange 134, using different combinations of matching bolt holes in plates 134 and 148. A piston rod 156 extends downwardly from the cylinder 152 and carries a suitable groundcontacting supporting element which in this case is illustrated as a caster wheel 158. Alternatively, a sliding shoe (not shown) may be substituted for the caster wheel.

When the reversing frame 58 is assembled on the leveling frame 54, pivot pin openings 126a and l26b in upper and lower webs 118 and respectively, are in vertical alignment with the sleeve bearing 112. A pivot pin 113 is fitted through the vertically aligned openings 126a and 126b and is held in, place by cotter pin 115, enabling the reversing frame to swing, relative to the leveling frame, about axis 60. As shown in FIG. 5, the lower web 129 of angle section 128 is retained in the recess 100 beneath the pad 96. A center opening 117 in that lower web will be aligned with an opening 121 in anchor member pad 96 when the reversing frame is centered for straight ahead operation. When the openings 117 and 121 are so aligned, a lock pin 123 may be dropped in place to hold the parts in this position.

Reversing cylinders are pivotally connected beneath the arched center portion of the anchor member 88 by means of pivot bolt 129. At their outer ends, the reversing cylinders have piston rods pivotally connected within brackets by pivot bolts 131.

The use and operation of the reversing cylinders 125 is conventional, so will not be described in detail nor will a hydraulic circuit be described for them. Briefly, coincident operation of these cylinders causes the reversing frame 58 to swing about pin 113, in one direction or the other. Normally, in operation, hydraulic fluid will be blocked within the cylinders to hold the reversing frame in any operative angular position without the necessity for any mechanical locking arrangement such as the pin 123. The latter is useful when the hydraulic system is inoperative, as for example when it is being trammed from one place of use to another.

As will be described in connection with the hydraulic control circuit, an important part of this invention is means for applying a predetermined maximum lifting pressure to the jacks 150, thereby transferring a definite, predetermined portion of the weight of the moldboard assembly to the caster wheels.

The moldboard assembly 62 comprises a plow moldboard 160 of conventional, forwardly concave, curved shape, having a vertical reinforcing rib 162 at each side and in the middle. There is-an additional pair of reinforcing ribs 164, of a special shape, at each side.

Each pair of reinforcing ribs'164 has a pair of horizontal hinge members 166,166, flanking each reversing frame hinge member 142. Each member 142 is pivotally connected between the corresponding pair of members 166 by hinge pin 170 held in place by cotter pin 172. At the center of the machine, a third hinged connection between the reversing frame 58 and moldboard assembly 62 is provided. This consists of a boss 166a fastened to the back of the moldboard and pivotally retained between the pair of hinge elements 142a by a hinge pin 174 and cotter pin 176.

A trip spring retainer, generally designated 178, is fastened as by welding across the back edges of each pair of reinforcing ribs 164. Each retainer is generally in the shape of a rectangular cup, with a back wall 185, bottom wall 180, side walls 182, and front wall 184, the latter being fastened to the reinforcing ribs 164 as by welding. The bottom wall 180 of each spring retainer 178 rests on a corresponding one of the seats 138. Within each retainer 178 are two upstanding coil springs 196, held by a U-shaped bolt 186, the base 187 of which is beneath the upper web 118 of the reversing frame. The vertical bolt stems 189 extend upward through openings 140 in the seat 138, and through openings 188 in the bottom of the spring retainer, and extend upward through openings 190 in spring compression plate 192. The plate is held by nuts 194 which may be adjusted to vary the compression of the springs 196. The compression of these springs varies the pressure of the retainers 178 against the seats 138.

Use and operation of trip springs 196 is no part of the present invention, so will not be described in detail. Briefly, however, they provide a useful safety feature, enabling the moldboard to be tripped, that is, displaced, upward, to a safe out-of-the-way position any time it strikes a hard obstruction such as a manhole cover, post, or curb. This is illustrated in FIG. 7 where the moldboard 160 is shown pivoting backward about axis 64 while the cable 242 lifts the entire assembly, as the moldboard strikes an obstruction 191.

Referring now to an important feature-of the invention, namely the convertibility of the snow plow, a steel blade 198 with a lower scraping edge 200 is fixed along the lower portion of the moldboard 160 by bolts 202. A second blade 204, made of rubber-like material, and having a scraping edge-206, is mounted on the moldboard for movement between extended and retracted positions in which the scraping edge of the rubber-like blade is respectively below and above the scraping edge of the steel blade. The term rubber-like as used here, includes all kinds of materials which may have a useful squeegee-like action on soft snow and slush when moved along the ground. It is intended to included reinforced or non-reinforced synthetic and natural rubbers and a wide variety of plastics materials such as polyurethane, which are softer than steel and thereby more capable of following imperfections and undulations in a paved surface. j

The rubber-like blade 204 is mounted along a transverse plate 208 which extends across the complete width of the moldboard, and is held in place by bolts 2l0-extending between a front, horizontal steel retaining strip 212, and the back plate 208. The plate 208 is strengthened at its midpoint by a transverse rib 214.

Refer now to FIG. 3. At two places on the back of the moldboard, below the pairs of reinforcing ribs 164, 164, there are pairs of generally triangular-shaped, vertical brackets 216. Each pair is spaced apart and fixed as by welding to the upper half of plate 208 and to the adjacent side of reinforcing rib 214. Each pair of brackets 216 has an upper pivot pin 218 pivotally journaled in a boss 220 welded to the back and underside of a transverse angle member 222 which reinforces the bottom portion of the moldboard.

A pair of actuating cylinders 224 swing the rubberlike blade 204 alternatively down to the operative position shown in solid lines in FIG. 3 and up to the stowed, out-of-the-way position shown in FIG. 4. In its operative position, the scraping edge 206 of. the rubber-like blade is below the scraping edge 200 of the steel blade. In its stowed position, the rubber-like edge is above the steel edge. V

Each cylinder 224 has, at its upper end, trunnions 226 pivotally engaged within spaced cylindrical gudgeons 228 which are fixed as by welding to the back edges of adjacent reinforcing ribs 164. The piston rod 230, depending from each cylinder 224 extends into the space between adjacent brackets 216 and is pivotally connected thereto by means of pin 232. Applying pressure fluid to the cylinders 224, beneath the pistons 234 through lower ports 236 moves the rubber-like blade 204 upward to its stowed position, shown in FIG. 4. Conversely, applying pressure fluid to the cylinders above the pistons 234 through upper ports 238 moves the rubber-like blade down to its operating position shown in FIG. 3 where the rubber-like scraping edge 206 is below the, steel edge 200 and engageable with the ground.

A lift and trip cable 242 is trained about sheave 46. Its upper end is looped around a pin 244 fastened to the center reinforcing rib 162 on the back of the moldboard. The lower end of the cable is fastened at the midpoint of a chain 246 (FIG. 2) connected to chain brackets248 bolted or welded to the top of transverse channel member 114.

The cable 242 serves two functions. It lifts the entire snow plow assembly, about axis 52 in response to fluid pressure applied to point 250 of lift cylinder 36. It also cooperates with the trip springs 196, and lifts the assembly when the moldboard strikes an obstruction. On impact, as shown in FIG. 7, the trip spring retainers 178 lift from seats 138 against the compression of the springs as the moldboard tilts forward about axis 64. This pulls the upper part of cable 242 forward and the lower part pulls the reversing frame upward so the plow will pass up and over the obstruction 191.

The hydraulic circuit for actuating the lift cylinder 36 and for actuating the reversing cylinders is not part of the present invention. It may be any conventional hydraulic arrangement readily devised by a person of ordinary skill so will not be described here.

The hydraulic circuit for actuating the movable rubber-like blade 204 and the caster wheels 158 is shown diagrammatically in FIG. 8. A control valve bank 256 is illustrated and this may consist of a conventional spool-type, three-way valve 258 having an output port 260 and operating handle 262, and a conventional spool-type, four-way valve 264 having input/output ports 266, 268 and operating handle 270.

The valve bank 256 is connected by a pressure line 271 to the outlet of a pump 272 and is connected by a return line 274 to a tank 276. The pump inlet is connected to the tank through supply line 278.

The handle 262 of valve 258 is manually operable between ON and OFF positions. In the ON position, fluid is directed under pressure into line 280 through relief valve 282 and thence to ports 284 of jacks 150 via lines 286, or to tank via line 288. Alternatively, pressure lines 280 may be connected directly into one of the branch lines 286, in which case an anti-backflow valve 287 may be used in line 280, or the valve 258 constructed to prevent backflow in the OFF position. Relief valve 282 may also be provided with an in-built check valve preventing backflow into line 280.

The handle 270 of valve 264 is manually operable between an OFF position and two ON positions. In one of the ON positions, fluid is directed under pressure from port 266 into line 290 and branch line 292 to the upper ports 238 of additional actuating jacks or cylinders 224, fluid being returned via branch lines 294 and line 296 to port 268 and thence to tank through line 274. In the other of the ON positions, fluid is directed under pressure from port 268 into line 296 and branch lines 294 into the lower ports 236 of actuating cylinders 224, fluid being returned vi'a branch lines 292 and line 290 to port 266 and thence to tank through line 274. In the OFF position, valve 264 blocks the return of fluid from both cylinders 224, thereby holding the rubber-like blade 204 in any selected position without the continuous application of pumped pressure fluid, or special locking mechanism.

Preferably, the valve bank 256 will be connected for open center operation, that is, when both operating handles 262 and 270 are in OFF positions, fluid is bypassed dir ectly from line 271 to line'74 274 minimum back pressure. This enables the system to operate with pump 272 running continuously while avoiding excessive heating of the hydraulic fluid.

Relief valve 282 is illustrated with a control wheel 298 which may be rotated to adjust the maximum pressure in the jacks 150.

Because pressure in jacks 150 tends to lift the snow plow, this effectively relieves the scraping edge 200 or 206, whichever is in use, from some of the weight of the moldboard assembly. This thereby transfers to the caster wheels 158 some portion of the weight of the moldboard assembly which would otherwise have to be supported by the scraping edge. In general, more pressure is required on the steel edge 200 for clearing hard snow and ice, than is required or desirable on the relatively softer edge 206 for clearing soft snow and slush. The control wheel 298 will preferably be placed in the cab of the vehicle, wth the other controls, so they can readily be operated by the driver, even while the vehicle is in motion.

In view of the foregoing description, use and operation of the device is deemed obvious. Briefly, to prepare the plow for operation in hard snow, it will first be lifted by applying pressure to the lift cylinder 36. Next, the angle of the moldboard will be adjusted by reversing cylinders 125 to displace snow to the right or left. The rubber-like cutting blade 204 will be lifted to its stowed position by moving valve handle 270 to the ON position to direct pressure fluid into the lower ports 236 of cylinders 224. The control wheel 298 will be adjusted for some preferred pressure for use with the steel blade. After a little use, the operator will know the best pressure to use under different operating conditions with each blade. Following the above-mentioned preliminary settings, the assembly will be lowered by the lift cylinder 36 until the caster wheels 158 and the steel scraping edge 200 bear against the ground. At this time, valve handle 262 will be moved to its ON position to direct fluid under pressure into the jacks 150. This will transfer a certain predetermined portion of the weight of the assembly from the blade to the caster wheels and this portion is readily adjusted by the wheel 298. By use of the relief valve 282 in the combination shown, any excess pressure, above the relief valve setting, supplied through line 280 from the pump, will merely be diverted through line 288 to tank. It should be emphasized that the caster wheel jacks 152 are primarily weight transferring devices, diverting some but not all the weight from the moldboard blade to the caster wheels in accordance with the operators judgment under the working conditions encountered.

Readying the plow for use with the rubberJike blade 204 is carried out in exactly the same manner as described above for the steel blade except that the valve handle 270 will be moved to the other ON position to direct fluid under pressure through line 290 into the upper ends of cylinders 224. This moves the blade 204 down to the operating position shown in FIG. 3. Generally, with rubber-like blade 204, the pressure in the caster wheel jacks will be selected somewhat higher, by means of the control wheel 298, than for the steel blade, to transfer a greater portion of the weight of the moldboard assembly from the rubber-like blade to the caster wheels.

It will'be apparent that the embodiment shown is exemplary only and that many specific changes and modifications can be made in construction and arrangement within the scope of the invention as defined by the appended claims.

I claim:

1. A convertible snow plow comprising:

a moldboard assembly including a moldboard having first and second blades, each having a scraping edge selectively engageable with the ground;

said first blade being rigid and fixed along the lower portion of said moldboard;

said second blade being rubber-like and mounted on said mold-board for movement between extended and retracted positions in which the scraping edge of the second blade is respectively below and above the scraping edge of the first blade;

means for moving said second blade between said extended and retracted positions and for holding said second blade selectively in one of said positions;

said moldboard assembly having horizontal pivotal connecting means on an axis transverse to the longitudinal centerline and spaced to the rear of said moldboard enabling attachment to a vehicle for up and down tilting adjustment of the moldboard assembly relative to the vehicle about said pivotal connecting means;

hydraulic jacks mounted between the moldboard and v the pivotal connecting means at opposite sides of the longitudinal centerline of the moldboard assembly and having ground-contacting supporting elements vertically movable to elevate the moldboard in response toflow of pressure fluidto said jacks;

9 hydraulic control circuit means including a pump connected with said jacks through control valve means for directing fluid under pressure to said jacks to thereby exert a lifting force on the moldboard assembly through said ground-contacting supporting elements; and relief valve means connected with said jacks effective to limit the pressure supplied to said jacks to a value transferring a definite, predetermined portion less than the total of the weight of the moldboard assembly to said ground-contacting supporting elements, thereby limiting the weight of the moldboard assembly supported by either of said first or second blades in accordance with the pressure rating of said relief valve means while maintaining said blade in operative engagement with the ground.

2. A convertible snow plow according to claim I having additional hydraulic jacks connected between said moldboard and said second blade, and said hydraulic control circuit means includes additional control valve means movable to two operative positions for directing fluid under pressure selectively to opposite ends of said additional jacks for moving said second blade between said extended and retracted positions, said additional control valve means being actuatable to an OFF position blocking the flow of fluid from said additional jacks to hold said second blade selectively in its said extended and retracted positions.

3. A convertible snow plow according to claim 1 in which said second blade is supported at the rear of said moldboard by a horizontal pivotal mounting and is vertically swingable between its said extended and retracted positions.

4. A convertible snow plow according to claim 3 having additional hydraulic jacks connected between said moldboard and said second blade, and said hydraulic control circuit means includes additional control valve means movable from an OFF position to either of two ON positions for selectively directing fluid under pressure to opposite ends' of said additional jacks for moving said second blade to said extended and retracted positions, said additional valve means being effective in said OFF position to block the back flow of fluid from said additional jack means to hold said second blade selectively in either extended or retracted position.

5. A convertible snow plow according to claim 1 in which said ground-contacting supporting elements are caster wheels.

6. A convertible snow plow according to claim 1 in which said hydraulic control circuit means includes a tank connected to the outlet of said relief valve means and between said pump and said jacks, a three-way valve connected respectively to said pump and tank and relief valve, said three-way valve being movable to an ON position effective to direct pressure fluid from said pump to said jacks and thereby exert a lifting force on said moldboard assembly.

7. A convertible snow plow according to claim 6 having additional hydraulic jacks connected between said moldboard and said second blade, and said hydraulic control circuit means includes a four-way valve connected respectively to opposite ends of said additional hydraulic jacks and tank and pump, said four-way valve being movable to two ON positions for directing fluid under pressure selectively to opposite ends of said additional jacks for moving said second blade to said extended and retracted positions while returning fluid from the opposite ends to tank, and said four-way valve being movable to an OFF position blocking return of fluid from either end of said additional hydraulic jacks to tank to thereby hold said second blade selectively in its said extended and retracted positions.

UNITED STATES PATEN'I OFFICE ;CER'1IFICA'1E OF CORREC'IION Patent No. 3 I Dated February 26 1 974 lnvb c'ofls) Roderick C. Snyder It is certified that error appears in the above-idcntified patent and that said Letters Patent are hereby corrected as shown below:

F L I Col. 1, 1.28, "undulatlon" should be -undulat1ons--;

. 1.63, after "rubber" insert ,-like blade-m Col. 3, 1.14, "pivor" should be --pivot-;'

l .2l,' "ahd" should be -and--;

1.38, '"providedi should be --provides-.

Col. 7, l .l0, "lines" should be line-; 1.36 U "74 274" should be --274-.

Signed end sealed this 6th day of August 1971+.

(SEAL) Afctest:

MoCOY M. GIBSON, JR. c. MARSHALL -DANN Attesting 'Officer A Commissioner of Patents 

1. A Convertible snow plow comprising: a moldboard assembly including a moldboard having first and second blades, each having a scraping edge selectively engageable with the ground; said first blade being rigid and fixed along the lower portion of said moldboard; said second blade being rubber-like and mounted on said moldboard for movement between extended and retracted positions in which the scraping edge of the second blade is respectively below and above the scraping edge of the first blade; means for moving said second blade between said extended and retracted positions and for holding said second blade selectively in one of said positions; said moldboard assembly having horizontal pivotal connecting means on an axis transverse to the longitudinal centerline and spaced to the rear of said moldboard enabling attachment to a vehicle for up and down tilting adjustment of the moldboard assembly relative to the vehicle about said pivotal connecting means; hydraulic jacks mounted between the moldboard and the pivotal connecting means at opposite sides of the longitudinal centerline of the moldboard assembly and having groundcontacting supporting elements vertically movable to elevate the moldboard in response to flow of pressure fluid to said jacks; hydraulic control circuit means including a pump connected with said jacks through control valve means for directing fluid under pressure to said jacks to thereby exert a lifting force on the moldboard assembly through said ground-contacting supporting elements; and relief valve means connected with said jacks effective to limit the pressure supplied to said jacks to a value transferring a definite, predetermined portion less than the total of the weight of the moldboard assembly to said ground-contacting supporting elements, thereby limiting the weight of the moldboard assembly supported by either of said first or second blades in accordance with the pressure rating of said relief valve means while maintaining said blade in operative engagement with the ground.
 2. A convertible snow plow according to claim 1 having additional hydraulic jacks connected between said moldboard and said second blade, and said hydraulic control circuit means includes additional control valve means movable to two operative positions for directing fluid under pressure selectively to opposite ends of said additional jacks for moving said second blade between said extended and retracted positions, said additional control valve means being actuatable to an OFF position blocking the flow of fluid from said additional jacks to hold said second blade selectively in its said extended and retracted positions.
 3. A convertible snow plow according to claim 1 in which said second blade is supported at the rear of said moldboard by a horizontal pivotal mounting and is vertically swingable between its said extended and retracted positions.
 4. A convertible snow plow according to claim 3 having additional hydraulic jacks connected between said moldboard and said second blade, and said hydraulic control circuit means includes additional control valve means movable from an OFF position to either of two ON positions for selectively directing fluid under pressure to opposite ends of said additional jacks for moving said second blade to said extended and retracted positions, said additional valve means being effective in said OFF position to block the back flow of fluid from said additional jack means to hold said second blade selectively in either extended or retracted position.
 5. A convertible snow plow according to claim 1 in which said ground-contacting supporting elements are caster wheels.
 6. A convertible snow plow according to claim 1 in which said hydraulic control circuit means includes a tank connected to the outlet of said relief valve means and between said pump and said jacks, a three-way valve connected respectively to said pump and tank and relief valve, said three-way valve being movable to an ON position effective to direct pressure fluid from said pump to said jacks and thereby exert a lifting force on said moldboard assembly.
 7. A convertible snow plow according to claim 6 having additional hydraulic jacks connected between said moldboard and said second blade, and said hydraulic control circuit means includes a four-way valve connected respectively to opposite ends of said additional hydraulic jacks and tank and pump, said four-way valve being movable to two ON positions for directing fluid under pressure selectively to opposite ends of said additional jacks for moving said second blade to said extended and retracted positions while returning fluid from the opposite ends to tank, and said four-way valve being movable to an OFF position blocking return of fluid from either end of said additional hydraulic jacks to tank to thereby hold said second blade selectively in its said extended and retracted positions. 